The present invention relates generally to the field of implant dentistry, and in particular to a new and useful pick-up implant abutment.
Impression copings are used to register the position of a dental implant placed into a patient's jaw. Two types of impression copings are used for implant level indexing.
The first type of impression coping is called a transfer coping which remains on an implant after the impression material is removed from the mouth. It is then removed from the implant, attached to the implant analog and inserted back into the impression. This technique is called the “closed tray method.” There are several factors which influence the accuracy of the closed tray method.
One factor is that it is impossible to machine the implant engaging parts of the impression coping and the implant abutment to be the same. A second factor is that it is impossible to machine the abutment engaging parts of the implant analog and the implant to be the same. Thirdly, some degree of impression material distortion always occurs during removal and re-insertion of the coping into the hardened impression material. This prevents accurate seating of the coping inside the impression.
A fourth factor is due to manufacturing tolerances. It is impossible to mate the implant analog with the implant abutment in exactly the same position as will be done with the implant and implant abutment later in the patient's mouth. A fifth factor is due to severe distortion of the impression material that occurs upon removal of the impression tray when multiple angulated implants are present.
The second type of implant impression or indexing is called the “open tray method” which eliminates the third and fifth factors. Impression coping used in this method is called pick-up coping, since it stays inside the impression material after the impression is removed from the mouth. The use of an elongated fastener and the hole made in the impression tray provide the means to disengage the coping from the implant and allow the removal of the impression from patient's mouth. The coping remains inside the impression material.
Though more accurate than the closed tray method, the open tray method still does not solve the three other problems noted above.
There is a need for a new abutment and method for taking an implant level impression which would eliminate the negative effect of size discrepancy between implant and implant analog, abutment and abutment analog and would also have the benefits of an open tray impression method.
The use of pick-up or transfer copings can be especially detrimental with locking taper implants (an example is described in the inventors co-pending international patent application PCT/US2007/074847 filed Jul. 31, 2007, and his U.S. patent application Ser. Nos. 11/615,131 filed Dec. 22, 2006, and 12/092,900 filed May 7, 2008) due to the sliding nature of the mating components. Discrepancies in diameter between the internal locking taper bore of the impression coping and the locking taper bore of the abutment will be multiplied several times due to sliding nature of the locking taper connection. A difference of only 6 microns will lead to a 100 microns difference in a vertical dimension (distance between the abutment or the impression coping, and the implant shoulder) between the impression coping/implant assembly and abutment/implant assembly. Current machining tolerances are much greater than 6 microns. If conventional impression methods are used, the discrepancy can be as high as 0.3 mm.
U.S. Pat. No. 5,106,300 to Voitik teaches the use of impression coping that is attached to the implant abutment and is picked up together with the abutment in the impression tray during an impression taking step. The open tray impression method is advocated by the inventor. Although more accurate then other described methods, this method also presents multiple challenges. Impression coping has to be used; impression coping has to be stocked in different sizes for abutments of different diameters and lengths; impression coping has to be properly attached to the abutment; and impression coping can separate from the abutment during impression removal because the fastener connecting the impression coping to the abutment and the implant has to be removed.
Known locking taper connection systems use conventional impression methods which produce inaccurate and unpredictable results.
An implant known as the Nobel Active external, was introduced in 2007 by Nobel Biocare AB, of Göteborg, Sweden, the largest implant manufacturer in the world. It has a 3 degree locking taper post and an indexing element in the form of a hex positioned on its end. The mating abutment has an internal 3 degree tapered bore and an internal indexing hex. The manufacturer realized that the use of impression coping would not yield an accurate result, so the standard crown and bridge impression method was advocated. The abutment is prepared by the dentist, tapped over the implant and an impression of the abutment is then taken and is sent to the laboratory for prosthesis fabrication. It is universally accepted that the use of implant level impression coping is much preferred in implant dentistry over the standard crown and bridge method.
Impladent Ltd. of Holliswood, N.Y., is an external locking taper implant manufacturer that also relies on the standard crown and bridge impression method.
The Bicon implant system (from Bicon Dental Implants of Boston, Mass.) uses implants having an internal locking taper bore and abutments with an external locking taper post. Bicon introduced the use of a plastic impression post which is tapped into the bore of the implant and is picked up by the impression material. The implant analog is than tapped over the post, and the abutment is tapped into the implant analog. During the prosthesis delivery appointment the abutment is tapped into the implant while the custom made acrylic jig restricts the rotational movement of the abutment. Many factors make accurate indexing impossible, however, the most critical ones being the inability of the operator to control tapping force and the difference in diameter between the implant analog and the implant, which affects the vertical positioning of the abutment. The abutment may seat more or less into the implant well, up to 0.1-0.2 mm, when compared to the implant analog.
It has been shown that accurate (i.e. within 0-10 microns range) repeated vertical connection between locking taper abutments and implants can only be achieved if:
1) the same abutment is mated with the same implant; and
2) the same amount of force is applied to activate the locking taper connection.
Accordingly a need remains for an improved pick-up implant abutment and the new method of implant position indexing that avoid the problems of the prior art.